Purpose: Determination of pressure derived myocardial fractional flow reserve(FFR) has been proposed as a means to assess stent deployment. We investigated the relative value of FFR by comparing it with the intravascular ultrasound(IVUS) for evaluating optimal sirolimus-eluting stent(SES) implantation. Methods: In 46 patients, a SES was implanted in 51 lesions located at proximal to mid coronary arteries followed by optional adjuvant dilatation with non-compliant high-pressure balloon. IVUS assessment and FFR measurement were performed before and after the interventional procedure. Results: Receiver operator characteristic analysis defined a optimal FFR cut point at > 0.94 for the prediction of optimal stent deployment based on validated IVUS criteria(final minimal lumen area(MLA) ��� 5mm²); at this threshold, the sensitivity, specificity, and predictive accuracy of FFR were 50%, 78%, and 62%, respectively. Both optimal IVUS and FFR results were achieved in 27 lesions(group A) but, 15 lesions had optimal IVUS and suboptimal FFR results(group B). Plaque burden, reference lumen area, final MLA and final minimal lumen diameter were not different between both groups. Length of stented segments was longer(56 vs. 43mm, p=0.023) in group B than group A. Conclusions: An FFR > 0.94, measured after SES deployment, predicts an optimal result. however, an FFR ��� 0.94 does not reliably predict an suboptimal stent result. In patients treated with multiple long SES implantation, an FFR might underestimate the stent result, compared it with IVUS.